The present invention is directed to the field of thermostat placement brackets. More particularly, the present invention is directed to a bracket assembly and method for positioning a cooling fan thermostat on a motorcycle engine.
Air-cooled motorcycle engines normally incorporate cooling fins on each cylinder in order to increase both the conductive and convective dissipation of waste heat. As a motorcycle travels, air flows over the cooling fins and increases the fins"" heat dissipating efficiency. However, this increase in efficiency lasts only as long as a constant airflow continues to pass over the cooling fins. When the motorcycle is traveling or idling at low speeds, airflow over the cooling fins is reduced or eliminated, significantly limiting the ability of the cooling fins to dissipate heat. If an engine is operated for extended periods, under extreme conditions, or in an environment that is enclosed or partially shielded from the wind, overheating and subsequent engine failure or damage can result.
In order to improve air flow and thereby improve heat dissipation from the surfaces of an engine""s cooling fins, cooling fans are often installed as optional equipment on motorcycles. Such fans are typically operated with a thermostat and are positioned to draw in and blow air laterally across each of the engine""s cylinders. If during operation, a motorcycle""s forward movement produces sufficient air flow to remove most of the excessive waste heat generated, it is possible that no additional heat dissipation will be necessary. If however, air flow is reduced due to idling, insufficient speed, extreme conditions, or an obstruction, waste heat will likely be generated faster than it can be dissipated by the cooling fins working alone. Therefore, a cooling fan""s thermostat will normally be set to operate the cooling fan as soon as the engine""s temperature surpasses a preselected maximum temperature. Once the cooling fan begins to operate, air continues to blow across the cooling fins, convectively removing heat from the surfaces of the cylinder and cooling fins and until the thermostat senses that temperature has been reduced below the preselected maximum level.
In prior art engines, such as the engine 10 depicted in FIG. 2, a cooling fan assembly (not shown) houses a fan (not shown) positioned to draw air over the engine""s cylinders 20, the cylinders 20 being positioned on an engine block 22. As depicted in the side view of the same engine in FIG. 3, the fan draws and blows air 14 against the cylinders 20 and over the cylinders"" cooling fins 18. The fan is operated by a thermostat 23 placed on an air cleaner housing 12. The thermostat 23 is placed at a position most proximate the cylinders 20 while still being positioned on the air cleaner housing 12. As best understood with reference to FIG. 3A, this positioning puts the thermostat 23 in the line of the flowing air 14. The thermostat 23 also remains separated from the engine block 22 and cylinders 20 by a substantial distance without having a direct structural interconnection.
Such previous configurations significantly limit the thermostat""s temperature sensing ability. One result of the configuration is that heat must first convectively migrate the distance from the engine""s cylinders 20 to the air cleaner housing 12 before it can be sensed by the thermostat 23, significantly delaying the thermostat""s response time in reacting to temperature changes of the engine 10. Another result is that plastic and other materials which comprise the air cleaner housing 12 which surround the thermostat 23 tend to both insulate the thermostat 23 and dissipate ambient and radiant heat, further delaying the thermostat""s response time to temperature changes and possibly subjecting the thermostat 23 to premature cooling. Such possible premature cooling can cause the cooling fan to shut off before the engine""s temperature falls to below the preselected maximum level. Consequently, the lowered thermostat responsiveness of such previous designs inherently limits a fan""s ability to effect engine cooling and to prevent overheating.
The present invention is a bracket assembly and method for positioning a cooling fan thermostat on a motorcycle engine so that the mounted thermostat is more responsive to actual changes in engine temperature. A bracket mounts on the engine""s engine block near the base of the cylinders and positions the thermostat close to the cylinders"" cooling fins. This positioning leaves the thermostat well below the lines of air flowing from the fan and prevents the thermostat from cooling before lowering the engine temperature below the preset maximum level. This positioning also leaves the thermostat closer to the cylinders which are themselves the most significant sources of heat in the engine, making the thermostat more convectively responsive to the engine""s actual temperature.
The bracket and/or the components of the bracket assembly may be made of a thermally conductive material. The bracket provides a single structural link between the engine block and the thermostat, permitting more efficient and conductive heat transfer between the engine and thermostat. Thus, the invention permits the thermostat to be both convectively and conductively more responsive to the engine temperature.
Some motorcycle engines have preexisting studs extending outward from the engine block near the bases of the cylinders. In such engines, a bracket assembly can be mounted by fitting a bracket over the existing stud and securing the bracket in position with a nut and washer. Many such engines have adjacently positioned screw caps which can interfere with the positioning of the bracket. Thus, some embodiments of the invention include shaved edges on the bracket and/or on some of the bracket assembly components to provide clearance against the cap screws. In some of these embodiments, one of the shaved edges can be positioned sufficiently proximate the screw cap to restrict undesired rotational movement of the bracket.
In other embodiments of the invention, a threaded mounting hole is added to an engine block if the engine lacks a stud near the base of its cylinders. These embodiments incorporate a threaded mounting bolt to fasten the bracket to the engine block. In some of these embodiments, a spacer is added to provide clearance between the bracket and engine block if such clearance is necessary to properly orient the bracket with respect to the cylinders.
Those skilled in the art will realize that this invention is capable of embodiments which are different from those shown and described below. It will be appreciated that details of the structure of this cooling fan thermostat bracket can be changed in various manners without departing from the scope of this invention. Accordingly, the drawings and Detailed Description of the Preferred Embodiments below are to be regarded as including such equivalent thermostat brackets as do not depart from the spirit and scope of the invention.